The present invention relates to a method for modification of properties of substrates by irradiating substrates to be modified with accelerated ions, and an apparatus used therefore.
The following methods have been known as conventional surface modification methods, especially for modification of the surface of aluminum or alumina to produce aluminum nitride.
For example, Japanese Patent Kokai No. 60-60910 discloses a method for producing aluminum nitride which comprises treating a mixture of alumina powder and carbon powder at a very high temperature of 1400.degree.-1700.degree. C. for a long time of 3-10 hours in a nitrogen or ammonia atmosphere. This method utilizes a thermal equilibrium reaction at high temperature and this is a general method in conventional surface modification. However, this method requires a large plant investment besides a large maintenance cost. In addition, workability is low and, thus, this method is unsatisfactory in practical application.
Furthermore, Japanese Patent Kokai No. 62-128989 discloses a method which comprises subjecting a sintered alumina plate to low-temperature plasma treatment in an atmosphere of nitrogen-hydrogen mixed gas to form an aluminum nitride thin film on the surface of the sintered alumina plate. According to this method, although aluminum nitride film is formed on the substrate surface in a relatively short time of 1 hour, the film is formed in the mixed gas atmosphere under a very high pressure of 10 Torr after evacuation of the chamber until the pressure in the chamber reaches 0.01 Torr and hence many impurities are contained. Furthermore, the temperature for plasma treatment is as low as 800.degree.-950.degree. C. Thus, this method also has problems in practical use.
Other methods for production of aluminum nitride are formation of aluminum nitride on the surface of metallic aluminum by plasma jetting or arcing. However, these methods require a high temperature and a high pressure and have problems in practical use like the above-mentioned methods.
Furthermore, as methods for modification of the surface of metallic or non-metallic materials, especially at a relatively low temperature of from room temperature to a few hundred .degree. C., there have been known an ion plating method and a dynamic mixing method which comprises simultaneously carrying out ion irradiation and vapor deposition. The ion plating method comprises ionizing metal vapor and depositing it on a material and the dynamic mixing method comprises simultaneously carrying out vapor deposition of metal vapor on a material and ion implantation. These methods both carry out coating on the surface of materials to be treated and do not modify the materials by changing the properties of the materials.
As explained above, the conventional methods utilize thermal equilibrium reaction or plasma and require a considerably high temperature for the treatment and do not give any consideration to plant investment, maintenance cost, operating facility, and treatment of materials combined with materials of relatively low melting point Thus, these methods have problems for practical applications.
Moreover, according to the latter conventional methods, a treatment at a relatively low temperature is possible utilizing ionization and ion irradiation, but basically these methods merely carry out coating of the surface of materials and do not give any consideration to modification of materials in a real sense.